Meh, Season 3 (plus the whistle blowing) convinced me that the series I want died with Monty. I might pick it back up if I hear good news about Season 4, but otherwise my hype train ticket has been thrown away.

Basically all deaths of season three can be reversed.
Torchwick might burst out of the Grimm like the black market dude from Pacific Rim in the end.
Penny is a robot as long as there is a second body, her memory chips could be implanted in it and she would revive.
Honestly, I think Ironwood or someone in his country had different intentions regarding Penny, Amber and the machine below beacon. Just think about it, Penny might be easily controlled in some kinda way since she is a machine, but thanks to her soul it might be possible to transfer the maidens power to her.
Now unlike a normal maiden she would never truly die of old age, so the power is eternaly bound to her and the faction controlling her.

Pyrrha might comeback through some Maiden hijinks.
Amber wook up and looked to Pyrrha's side when they started the machine.
It might be that at that moment she chose her despite not knowing her name as her successor for her bravery to sacrifice literally "herself".
So once the unrightfull owner of the power dies the power will try to go to the maiden it was set to go to which is Pyrrha and thus recover her body in some magic way.

I think torchwick will be all ****** in but still comeback, spare parts sticking to his face and ****, and end up becoming a completely abusive asshole instead of a cheeky crook.
Penny is most likely alive, lets be fair, the reason we saw a scene of the guy who made her right after she died was to implied that they were gonna rebuild her better, they have the technology.

Pyrrha however...
I have 2 theories on that:
1: She aint dead. when Cinder fights Os in the basement, he somehow dissappears but not through the elevator, as we see Cinder destroy that on her way up. that was no other way in or out and Cinder most likely didnt just let him leave anyways. There is a slight of chance that Cinders "Incinaration" move is simply a form of forced teleport, used on Os and Pyrrha to bring them to Salem.

2: Pyrrha dies, gets reborn as some type of grimm which Jaun eventually has to kill in and epic "the student becomes the master" fight type deal.